DO NOT MERGE: [libc++] Move __clamp_to_integral to <cmath>, and harden against min()/max() macros

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@370900 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 87e6185621d332d2ef8695b94778663380c83bb9)

Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=994957
Bug: http://b/139690488
Change-Id: Ice92a8ea6f675be069a70c5ad1003cf99b4fc474
(cherry picked from commit 82e0483c4a47233ed2f7bab545b32e5ddd474e59)
(cherry picked from commit 21beede0ddfffab3e31961a68f7282b54f3ab52a)

3 files changed, 51 insertions, 34 deletions

diff --git a/include/cmath b/include/cmath
index 74b4ab8a8..6a081b560 100644
--- a/include/cmath
+++ b/include/cmath
@@ -303,6 +303,8 @@ long double    truncl(long double x);
 
 #include <__config>
 #include <math.h>
+#include <limits>
+#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
@@ -612,6 +614,36 @@ __libcpp_isfinite(_A1 __lcpp_x) _NOEXCEPT
     return isfinite(__lcpp_x);
 }
 
+template <class _IntT, class _FloatT,
+    bool _FloatBigger = (numeric_limits<_FloatT>::digits > numeric_limits<_IntT>::digits),
+    int _Bits = (numeric_limits<_IntT>::digits - numeric_limits<_FloatT>::digits)>
+_LIBCPP_INLINE_VISIBILITY
+_LIBCPP_CONSTEXPR _IntT __max_representable_int_for_float() _NOEXCEPT {
+  static_assert(is_floating_point<_FloatT>::value, "must be a floating point type");
+  static_assert(is_integral<_IntT>::value, "must be an integral type");
+  static_assert(numeric_limits<_FloatT>::radix == 2, "FloatT has incorrect radix");
+  static_assert(is_same<_FloatT, float>::value || is_same<_FloatT, double>::value
+               || is_same<_FloatT,long double>::value, "unsupported floating point type");
+  return _FloatBigger ? numeric_limits<_IntT>::max() :  (numeric_limits<_IntT>::max() >> _Bits << _Bits);
+}
+
+// Convert a floating point number to the specified integral type after
+// clamping to the integral types representable range.
+//
+// The behavior is undefined if `__r` is NaN.
+template <class _IntT, class _RealT>
+_LIBCPP_INLINE_VISIBILITY
+_IntT __clamp_to_integral(_RealT __r) _NOEXCEPT {
+  using _Lim = std::numeric_limits<_IntT>;
+  const _IntT _MaxVal = std::__max_representable_int_for_float<_IntT, _RealT>();
+  if (__r >= ::nextafter(static_cast<_RealT>(_MaxVal), INFINITY)) {
+    return _Lim::max();
+  } else if (__r <= _Lim::lowest()) {
+    return _Lim::min();
+  }
+  return static_cast<_IntT>(__r);
+}
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif  // _LIBCPP_CMATH
diff --git a/include/math.h b/include/math.h
index b61c2253d..b7659267e 100644
--- a/include/math.h
+++ b/include/math.h
@@ -1426,40 +1426,6 @@ trunc(_A1 __lcpp_x) _NOEXCEPT {return ::trunc((double)__lcpp_x);}
 
 #endif // !(defined(_LIBCPP_MSVCRT) && ((_VC_CRT_MAJOR_VERSION-0) < 14))
 
-_LIBCPP_BEGIN_NAMESPACE_STD
-
-template <class _IntT, class _FloatT,
-    bool _FloatBigger = (numeric_limits<_FloatT>::digits > numeric_limits<_IntT>::digits),
-    int _Bits = (numeric_limits<_IntT>::digits - numeric_limits<_FloatT>::digits)>
-_LIBCPP_INLINE_VISIBILITY
-_LIBCPP_CONSTEXPR _IntT __max_representable_int_for_float() _NOEXCEPT {
-  static_assert(is_floating_point<_FloatT>::value, "must be a floating point type");
-  static_assert(is_integral<_IntT>::value, "must be an integral type");
-  static_assert(numeric_limits<_FloatT>::radix == 2, "FloatT has incorrect radix");
-  static_assert(_IsSame<_FloatT, float>::value || _IsSame<_FloatT, double>::value
-               || _IsSame<_FloatT,long double>::value, "unsupported floating point type");
-  return _FloatBigger ? numeric_limits<_IntT>::max() :  (numeric_limits<_IntT>::max() >> _Bits << _Bits);
-}
-
-// Convert a floating point number to the specified integral type after
-// clamping to the integral types representable range.
-//
-// The behavior is undefined if `__r` is NaN.
-template <class _IntT, class _RealT>
-_LIBCPP_INLINE_VISIBILITY
-_IntT __clamp_to_integral(_RealT __r) _NOEXCEPT {
-  using _Lim = std::numeric_limits<_IntT>;
-  const _IntT _MaxVal = std::__max_representable_int_for_float<_IntT, _RealT>();
-  if (__r >= ::nextafter(static_cast<_RealT>(_MaxVal), INFINITY)) {
-    return _Lim::max();
-  } else if (__r <= _Lim::lowest()) {
-    return _Lim::min();
-  }
-  return static_cast<_IntT>(__r);
-}
-
-_LIBCPP_END_NAMESPACE_STD
-
 } // extern "C++"
 
 #endif // __cplusplus
diff --git a/test/libcxx/numerics/c.math/undef_min_max.pass.cpp b/test/libcxx/numerics/c.math/undef_min_max.pass.cpp
new file mode 100644
index 000000000..ba1696eb2
--- /dev/null
+++ b/test/libcxx/numerics/c.math/undef_min_max.pass.cpp
@@ -0,0 +1,19 @@
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#if defined(__GNUC__) || defined(__clang__)
+#pragma GCC diagnostic ignored "-W#warnings"
+#endif
+
+#define min THIS IS A NASTY MACRO!
+#define max THIS IS A NASTY MACRO!
+
+#include <cmath>
+
+#include "test_macros.h"
+
+int main(int, char**) { return 0; }